A turn-off colorimetric DNAzyme-aptasensor for ultra-high sensitive detection of viable Cronobacter sakazakii

Cronobacter sakazakii is a typical food-borne bacterium that causes clinical symptoms including necrotizing enterocolitis, bacteremia, and meningitis with a mortality rate of 40 %-80 %. In this study, a pair of split G-rich DNA probes was assembled into the DNAzyme capable of mimicking peroxidase. The assembly was utilized to provide a simple, low-cost, highly specific, and sensitive method for rapid detection of viable C. sakazakii. In the absence of viable C. sakazakii, the two split G-rich DNA probes formed DNAzyme, mimicked the activity of peroxidase and displayed colorimetric signals to indicate detection results. In the presence of viable C. sakazakii, specific recognition by the aptamer results in the destruction of the DNAzyme-aptamer complex, and subsequently the colorimetric signal is "turned-off' due to the decrease in DNAzyme bioactivity. Under the optimal reaction conditions, there is a linear relationship between absorption intensity at 418 nm and logarithmic concentration of C. sakazakii in the range of 2-1200 CFU/mL (R-2 = 0.9839), with a detection limit of 1.2 CFU/mL. This is the highest sensitivity ever reported for viable C. sakazakii detection. Artificially contaminated samples were assayed by this novel sensor, and numerous advantages were discovered, including ultra-low sensitivity, low-cost, simple operation, and good performance, compared to existing methods. We believe the DNAzyme shows great potential for food safety applications.